Smartphones and other mobile computing devices are frequently “locked” after some period of inactivity to prevent an unauthorized user from accessing the contents of the device. Oftentimes, the mobile computing device displays a login image on a touchscreen with which the user may interact to enter a PIN or draw a certain pattern to gain access to the device. Depending on the particular embodiment, various mobile computing devices may be “unlocked” by entering a text-based password, swiping a repeatable pattern, shaking the device in a particular rhythm, tapping the display, using biometrics (e.g., fingerprints, facial recognition, iris recognition, etc.), and/or other suitable authentication techniques. However, many such authentication techniques are computationally intensive, time consuming, inconvenient for users, and/or have security weaknesses. For example, many user-preferred pattern-based authentication mechanisms (e.g., character/digit-based password entry, pattern swiping, etc.) involve the user touching the same portion of a touchscreen repeatedly, which often leaves easily analyzable fingerprint smudges.